size-diff CI step: make sure the toolchains for the old and new commits are both installed, otherwise the old commit will fail to build.
diff --git a/.github/workflows/size-diff.yml b/.github/workflows/size-diff.yml
index 4d14308..6f8c7d0 100644
--- a/.github/workflows/size-diff.yml
+++ b/.github/workflows/size-diff.yml
@@ -44,6 +44,7 @@
           git remote set-branches "${UPSTREAM_REMOTE_NAME}" "${GITHUB_BASE_REF}"
           git fetch --depth=1 "${UPSTREAM_REMOTE_NAME}" "${GITHUB_BASE_REF}"
           git checkout "${UPSTREAM_REMOTE_NAME}/${GITHUB_BASE_REF}"
+          rustup target add riscv32imc-unknown-none-elf thumbv7em-none-eabi
           make -j2 examples
           cargo run --release -p print_sizes >'${{runner.temp}}/base-sizes'